1. Field of the Invention
The present invention relates to an information processing apparatus, a printing apparatus, and an information processing method. More particularly, the present invention relates to a technique, in a system including an information processing apparatus such as a personal computer and a printing apparatus such as a printer, to process a tint block image for restraining a material printed by a printing apparatus from being copied.
2. Description of the Related Art
It is known to print content such as a form document or a resident card on special paper called copy protection paper which has been subjected to special printing to prevent or restrain an original material from being copied. In an original material, an image printed on copy protection paper is difficult for human eyes to perceive. However, if the original material is copied, a character string such as “Copy Inhibited” appears on a copied material. This causes a person who has copied the original material to hesitate to use the copied material. By letting the public know that form documents or the like are printed on copy protection paper, it is possible to cause persons to hesitate to copy form documents or the like.
However, a problem with copy protection paper is its high cost compared with plain paper. Another problem is that only a character string preprinted on copy protection paper during production of the copy protection paper appears on a copied material. This limits use of the copy protection paper.
Nowadays, various kinds of contents such as form documents, resident cards, etc. are produced in digital form. However, in many cases, at present, when contents are output, they are printed on plain paper using a printer.
In view of the above, much attention is now focused on a technique to produce copy protection paper using a computer and a printer instead of using a printing plate (see, for example, Japanese Patent Laid-Open No. 2001-197297). In this technique, when content produced using a computer is printed, image data called a tint block pattern is produced in addition to the content data, and the tint block pattern and the content data are printed in a superimposed manner. The tint block pattern is also called a copy-forgery-inhibited pattern. The tint block image on an original material (produced by using a printer) is perceived by human eyes as a simple pattern, a background image, or the like. However, if the original material is copied, a particular character string or a particular image appears on the copied material. Therefore, this feature of the original material restrains the original material from being copied, as with the special copy protection paper described above. Note that great advances in performance of printers have made it possible to achieve this technique.
When a tint block image producing using a computer is output such that the tint block image is superimposed on content data, it is possible to use ordinary paper on which to output the tint block image, and thus this technique is advantageous in terms of cost compared with the technique using forgery-protected paper. Furthermore, because it is allowed to produce a tint block image when content data is printed, it is possible to freely determine the color of the tint block image and a character string which will be visualized when an original printed material is copied. Another advantage is that information indicating date/time of printing and/or information specific to a printing apparatus can be used as a tint block image.
As described above, if an original printed material including a tint block image is copied, a particular character string or an image appears in a visible form on the copied material, whereby it is possible to suppress use of the copied material.
To achieve the above effects, a tint block image used herein basically includes two areas: a first area which is included in an original material and which will remain in a copied material; and a second area which is also included in the original material but which will disappear or will become low in intensity on the copied material compared with the intensity of the image in the first area. It is desirable that the tint block image be printed such that both areas have substantially the same intensity on the original material, and that a character string or the like which is hidden in the tint block image on the original material (and which will be visualized on a copied material) cannot be perceived by human eyes. This image area of the tint block image which is hidden in the original material but which will appear in a human-eye-visible form on a copied material is herein referred to as a latent mark (or a latent mark image). The image area which will disappear on a copied material or which will become low in intensity compared with the intensity of the latent mark visualized on the copied material is referred to as a background (or a background image). Thus, a tint block image basically includes a latent mark image and a background image. Note that the latent mark is also referred to as a foreground image, for example, when a user interface is discussed.
The latent mark image is formed of dots concentrated in a particular area. On the other hand, the background area is formed of dots dispersed in a particular area. Note that dots in these two areas are formed such that the density of dots is equal for these two areas so that it is difficult to distinguish the latent mark area and the background area from each other on an original material of the tint block image.
FIG. 10 shows a manner in which dots are formed in these two image areas. As shown in FIG. 10, a tint block image is composed of a background area in which dots are formed at dispersed positions and a latent mark area in which dots are formed at concentrated positions. The dots in these two areas can be formed using a halftone dot method under different conditions or a dither method under different conditions. For example, when a tint block image is produced using the halftone dot method, a latent mark area is produced using a small line density, while a background area is produced using a large line density. In the case in which the dither method is used, a latent mark area is produced using a dot-concentrated dither matrix, while a background area is produced using a dot-dispersed dither matrix.
In general, a scanner unit and a printing unit of a copier have a limitation on the reproduction ability depending on the input resolution of detecting small dots on a document or the output resolution of forming small dots on paper. If the background area of the tint block image is formed of dots with a size smaller than the lower resolution limit of the copier, and if the latent mark area of the tint block image is formed of dots with a size greater than the lower resolution limit of the copier, the dots of the latent mark area are reproduced on a copied material but the small dots of the background area are not reproduced. Because of this feature, if the tint block image is copied, the latent mark is visualized on the copied material. Hereinafter, the image visualized on the copied material will be referred to as a visualized image. Even if the background area is reproduced on a copied material, if the latent mark area on the copied material has a resolution that allows the latent mark area to be clearly perceived, it is possible to achieve an effect similar to that achieved when no dots are reproduced for the background area.
FIGS. 11A and 11B show a manner in which a latent mark is visualized. As can be seen from these figures, an image composed of concentrated dots is reproduced on a copied material, but an image composed of dispersed dots is not reproduced on the copied material.
Note that printing of a tint block does not necessarily need to be performed in the above-described manner, but a tint block may be printed in any manner if a visible character string or the like appears on a copied material. For example, a character string or the like may be formed in a background area so that the character string appears in an open shape (void shape) on a copied material. Note that in this case, the purpose of the tint block printing is also achieved.
The tint block is placed over the entire area (effective printing area) of a page so that it becomes possible to more effectively prevent an original material from being copied. Because the content of a document to be printed varies from page to page, a tint block is placed also in an area that does not overlap a document area so that a visualized image will appear over a large area thereby enhancing the capability of preventing the original material from being copied, and also enhancing the capability of adapting to variations in contents of pages.
However, placing a tint block over the entire area of a page results in an increase in the memory capacity necessary to render the tint block pattern and a decrease in the printing speed.